This invention relates generally to ribbon-like current-activated thermal transfer films which are used for non-impact printing.
The thermal transfer method of non-impact printing utilizes a current head which applies current to the exothermic resistance layer of the transfer film. Heat is generated when this current flows through the resistance layer. This heats the ink of the ink layer which is thereby transfered onto the recording medium, such as paper. This method is more advantageous than the old methods with respect to the energy used for recording. It is also better suited for recording colors of varying tones than the prior art method which employed a thermal head. Attention has recently been focused on the former method due to this superiority of the new method.
A printer, utilizing a similar type of current-applying thermal transfer film had been released to the media with the trademark QUIET WRITER. This new thermal transfer method created a sensation, as was reported in Denpa Shinbun Newspaper on Oct. 18, 1984. The technology of this commercial product has been disclosed in several U.S. Pat. Nos. including 4,103,066, 4,291,994, 4,384,797, and 4,453,839.
The new thermal transfer printing is so efficient that printing can even be made on rough transfer paper, such as paper having a Beck smoothness of about 4 seconds. Notwithstanding these advantages, the following problems with this type of transfer film used have arisen.
The ribbon generally utilized in this new thermal transfer printing has a dual layer structure. This structure includes a resistance layer and an ink layer. The ink layer adheres directly to the resistance layer and there is no intermediate support layer to add dynamic strength. Therefore, because the film's dynamic strength is so poor, it is easily stretched and it is fragile. It is fragile because the resistance layer is constructed by dispersing conductive carbon black in a resin-type binder. The ink layer is principally pigment and resin which lacks strength. Additionally, the method for producing such thermal transfer films is more complicated than previous methods, production rate is extremely low, and therefore the costs of the printing ribbons made from these films are higher than the costs for the old type of ribbon. These high costs fall heavily on the user.
Accordingly, it is desirable to provide an improved thermal transfer sheet which takes advantage of this new thermal printing method, but overcomes the problems outlined above.